Owada Tetsuo, Reading the letters of generals of the era of the Warring States (戦国武将の手紙を読む), Chuō Kōron, Tokyo, 2010
Tokugawa Ieyasu’s Vow – An appeal to Uesugi Kenshin
“I respectfully offer this vow.
Unable to hide my thoughts any longer, Gongendō, in the guise of a messenger, conveyed them to you. As such, I believe that you fully understand my intentions.
First, I have thoroughly considered the matter of Shingen’s betrayal, and I do not believe that any of it is false rumour.
Second, in order to facilitate an alliance between Nobunaga and Kagetora, I shall directly state my opinion to Nobunaga. As for talk of the union between Kōfu and Owari, I shall make insinuations to Nobunaga in order to prevent this from occurring.
Should I betray this vow, I am prepared to submit to the punishment of Śakra -devānam-Indra above and the Four Heavenly Kings below, all of the gods of Japan both great and small. In particular, Gongen of Izu and Hakone, the Great Deity of Mishima, Hachiman Daibosatsu, and all of the gods in residence at the Great Shine of Tenman.
The 8th day of the 10th month,
To Lord Uesugi”
A dispute over Tōtōmi
This is not your standard letter, but is a vow (or Kishōmon), written on sacred Go Ōhōin paper provided by Hakusan Gongen. It does not feature any yearly date, but was certainly written on the 8th of the 10th month of the 1st year of Genki (1570).
The title ‘Lord Uesugi’ (which uses a character variation on ‘sugi’, 椙) of course refers to Uesugi Kenshin (上杉謙信), who is also referred to as ‘Kagetora’ in the text. In short, this is a vow from Tokugawa Ieyasu to Uesugi Kenshin, created in order to attempt to forge an alliance. Ieyasu was already allied to Oda Nobunaga via the ‘Kiyosu’ pact (清須同盟), yet had decided to explore the possibility of creating an alliance with Kenshin. (126-127)
In the background to this activity lay the complicated relationship that Ieyasu had with Takeda Shingen. Two years before this vow was written, in the 12th month of the 11th year of Eiroku (1568), Ieyasu joined with Shingen and together they launched a simultaneous attack on Imagawa Ujizane, who was caught between the two. Shingen took hold of Suruga province, while Ieyasu gained control of Tōtōmi. Consequently Ieyasu’s territory extended from Mikawa all the way to Tōtōmi.
There is no evidence that Shigen and Ieyasu were bound together in a formal alliance, and it does appear that the military steps taken at the time were simply a combined effort to destroy the Imagawa. However Shingen, at this stage, was in a formal alliance with Nobunaga, and considering that Ieyasu and Nobunaga were also allied, Shingen and Ieyasu had an alliance of sorts, just not a direct one. (127)
As Shingen and Ieyasu did not share a direct alliance, after the Imagawa were overthrown Ieyasu’s relationship with Shingen underwent a dramatic turn. The Takeda army crossed the Ōi River, which marked the border between Suruga and Tōtōmi, and invaded Tōtōmi while simultaneously launching an invasion from Shinano province after traversing the Aokuzure Pass (which marked the border between Shinano and Tōtōmi). Needless to say, Ieyasu’s mistrust of Shingen had reached its peak by this time. (127)
All of the Tokugawa records written during the Edo period state that this move by Shingen was evidence of his ill-will towards Ieyasu. In particular, they emphasise that there was a secret agreement between Shingen and Ieyasu, known as the Sunen Bunkatsu Ryoyū (or Division of Suruga and Tōtōmi Territories). If such a secret agreement did exist, then Shingen had certainly acted with ill intent by advancing into Tōtōmi. However historical records of the Tokugawa household created during the Edo period were written with the intention of ‘deifying the ruler’, hence it is unclear whether any secret agreement did in fact exist. It may have been no more than an agreement to invade the Imagawa’s territory from east and west. (128)
Ieyasu certainly began to feel militarily threatened by Shingen. In the 1st year of Genki (1570), so as to ensure the conquest of Tōtōmi province, Ieyasu vacated his seat of Okazaki castle in Mikawa province in order to move into a castle in Tōtōmi province. His first choice for a site for the castle was at Mitsuke (見付). This area had previously functioned as a provincial capital, and was where the Shugo of Tōtōmi province, the Imagawa family, had established their headquarters. As such, it was the centre of politics in the province. (129)
However, not long after construction on the castle began, the relationship between Ieyasu and Shingen grew steadily worse, so much so that Ieyasu abandoned attempts to found a castle at Mitsuke and instead decided to build a new castle at Hikuma, and named it Hamamatsu castle. If Ieyasu had stayed at Mitsuke, he would have had the Tenryū River running to the west of the castle. If Shingen decided to attack him there, Ieyasu would have to contend with the Tenryū River at his back which would make his position more perilous, and Ieyasu was not keen on making a ‘final stand’. (129)
By moving to Hikuma, Ieyasu could ensure that the Tenryū River flowed to the east of the castle, and that if attacked by Shingen, the river would form a natural barrier. (129)
An alliance with Kenshin
It was at this time that Ieyasu was certainly perplexed with regard to Shingen, and this in turn led to his decision to send a vow to Kenshin. Of course, Shingen and Nobunaga were still bound by an alliance, as was Ieyasu himself to Nobunaga, hence Ieyasu put a lot of thought into how he might mitigate the threat from Shingen. The answer, it seems, was to make an alliance with Shingen’s rival, Kenshin. (129)
Ieyasu began to make initial moves towards an alliance in the 12th year of Eiroku (1569). He dispatched Gongendō (Kanō Bōkōhan, a priest) as a messenger to Kenshin to sound out Kenshin’s thinking on the possibility of an alliance. In the first line of the vow, Ieyasu’s clearly states that he has been betrayed by Shingen, while in the second he declares that he will work to sever the alliance between Nobunaga and Shingen. The alliance between Kōfu (Shingen) and Owari (Nobunaga) had been forged by this time, hence it might prove useful to explain how it came about and the implications this had for Ieyasu. (129)
Nobunaga, when he believed that an opponent was stronger than him, would not fight needlessly but would seek other means to increase his influence. This was certainly the relationship he had with Shingen. In the 11th month of the 8th year of Eiroku (1565), Nobunaga married off his niece to Shingen’s fourth son Katsuyori. Unfortunately, two years later, the niece died as a result of complications encountered during childbirth. Nobunaga considered severing his alliance with Shingen at this point, however he thought better of it and instead married off his eldest son Nobutada to one of Shingen’s daughters. This is the ‘union’ that Ieyasu refers to in his vow. As such, it shows just how well the alliance between Shingen and Nobunaga was progressing at this stage. (129)
Ieyasu makes it clear that in order to sever the union between Shingen and Nobunaga he would be prepared to insinuate rumours about Shingen. At the time, Shingen had not made any military advances against Nobunaga. This may have been because of the alliance shared between both sides, but may also have been because militarily Nobunaga was growing more powerful, and Shingen had decided that he could not simply attack Nobunaga with impunity. (129-130)
Ieyasu, on the other hand, was weak compared to Shingen and would be easier to overthrow. Shingen would have known that Nobunaga was also allied to Ieyasu, hence a decision to attack Ieyasu was a prime example of the logic of ‘survival of the fittest’. Ieyasu, as the daimyō of the provinces of Mikawa and Tōtōmi, certainly planned to continue his alliance with Nobunaga. Yet knowing full well that he could not match Shingen’s military prowess, he desperately sought an answer, and hit upon the idea of allying himself with Kenshin. (131)
At this time Ieyasu, in a letter dated on the same day as the vow, made his thoughts known to one of Kenshin’s senior retainers, Naoe Yamato no Kami Kagetsuna, in which he asked for ‘assistance’ should the time come. (131) According to the etiquette of the time, when a letter was sent from one individual to another, daimyō would communicate with other daimyō, while retainers would exchange letters with other retainers. However in this instance, Ieyasu sent letters to Kagetsuna via two of Kagetsuna’s own retainers, Sakai Tadatsugu and Ishikawa Kazumasa. This speaks volumes about the desperate straits in which Ieyasu now found himself. (132)
The Battle of Mikatagahara
Ieyasu certainly planned to keep his alliance with Kenshin a secret, however his activities caught the attention of Shingen. In the 3rd month of the 2nd year of Genki (1571), Shingen himself led a large army into Tōtōmi ostensibly to attack Kōtenjin castle. However, rather than going ahead with this plan, Shingen captured Kakegawa castle, Kuno castle, and Inui castle, as using them as forward posts, withdrew to Iida in Shinano province. (132)
This move, which allowed Shingen to draw Ieyasu into a false sense of security, then allowed Shingen to launch a new attack against Mikawa from the direction of Inoguchi. Nobunaga, who still retained his alliance with Shingen, did not wish to unnecessarily provoke an attack by Shingen, and told Ieyasu that he thought it best that he abandon Hamamatsu castle and withdraw to Yoshida castle in Mikawa. Ieyasu, knowing that ‘any retreat from Hamamatsu would mean humiliation as a warrior’, resolved to defend Hamamatsu castle to the death. (133)
At this time, although Ieyasu was in alliance with Kenshin, there was no possibility of Kenshin being able to send reinforcements to assist Ieyasu. It was simply too far to travel from Echigo to Mikawa and Tōtōmi in time. In the end, in the 12th month of the following 3rd year of Genki (1572), Shingen and Ieyasu met on the battlefield of Mikatagahara, which ended in total defeat for Ieyasu. (133)
Did Ieyasu now realise that his alliance with Kenshin was essentially worthless? Certainly, if one looks at it as an attempt to curtail the military power of Shingen, it was meaningless. Yet if one looks at things from a slightly longer time span, particularly in regard to the growing power of Nobunaga, then there was worth in forging an alliance with Kenshin. (133)
At the time of the Battle of Mikatagahara, Nobunaga sent 3,000 troops to Ieyasu as reinforcements. This development came to the attention of Shingen, who subsequently tore up his alliance with Nobunaga. In sum, as a result of the vow that Ieyasu to Kenshin, the two aims of the vow – to break up the alliance between Shingen and Nobunaga, and the marriage between Kōfu and Owari – both became a reality, and laid the foundation of the conflict between Takeda Katsuyori and Nobunaga/Ieyasu that would occur after Shingen’s death. (133)
One further note – hereafter Nobunaga attempted to forge an alliance with Kenshin himself. In the 2nd year of Tenshō (1574), Nobunaga sent the gift of a screen depicting the ‘Capital and its Surroundings’, painted by Kanō Eitoku, to Kenshin. (133)